Petra Diamonds has probably unearthed the largest diamond in its Cullinan mine in South Africa. It is a 122.52-carat rare blue diamond estimated to be worth £60 million.

The miner said it would analyse the rock before it would place it on the market after the end of June. It is expected to break the world record for the most expensive diamond for a 506-carat white stone sold at $35.3 million, New York Post reports.

The Cullinan mine is known for producing very large gems, but an industry nsider insider told Daily Mail that it is rare to unearth a blue stone that weights more than 100 carats. It was where the world's largest white diamond, weighing 3,106 carats, was unearthed in 1905.

It was initially discarded by the mine manager who thought it was too big to be a diamond but was eventually recovered and presented to King Edward VII in 1907. The centerpieces of the Crown Jewels came from that diamond.

A typical engagement ring often has a centerpiece diamond that usually weighs about on carat, and it is usually white.'